KR20160049880A - Cavity type low pass filter - Google Patents

Abstract

The purpose of the present invention is to provide a cavity-shaped low-pass filter which can reduce a full length comparatively and can increase a degree of freedom in design, thereby facilitating manufacture. The cavity-shaped low-pass filter according to the present invention comprises: L (inductance) elements composed in the structure of a transmission line having an inductance component and composed to be connected in a row; a housing having grooves formed at positions corresponding to at least part of the installation space of the L elements, connection points between the L elements, and points corresponding to the input and output of all the L elements; and C (capacitance) elements composed of structures for forming capacitance combining surfaces by facing the inner surfaces of the grooves, and connected directly or indirectly to at least part of the connection points between the L elements and the points corresponding to the input and output of all the L elements.

Description

Cavity type low pass filter (CAVITY TYPE LOW PASS FILTER)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless signal processing apparatus used in a wireless communication system, and more particularly to a cavity-type low pass filter (LPF).

Typically, a low pass filter (hereinafter abbreviated as " filter ") comprises a plurality of L (inductance component) elements serially connected between input and output ports of a signal and a plurality of L And a plurality of C (capacitance component) elements connected between the connection point and the ground terminal.

The low-pass filter can be structurally divided into a printed circuit board type and a cavity type. The low-pass filter of the printed circuit board type can be implemented using capacitors and inductors, which are common electronic circuit components that can be individually mounted on a printed circuit board, or a thin metal pattern corresponding to the L element and the C element, Or may be formed on a substrate.

 The cavity-type low-pass filter is formed of a box structure in which a cavity is formed through a metal housing and a cover. And a plurality of metal structures having a capacitance coupling surface facing the inner surface of the housing and the cover inside the box are provided as C elements. Further, a metal pin connecting the plurality of metal structures is provided as an L element. Such a cavity type filter is superior to a printed circuit board type filter in its characteristics and is suitable for high power equipment and is widely applied to a base station, a repeater, and the like in a mobile communication system, for example.

Fig. 1 is a perspective view of a conventional low-pass filter of a cavity type, Fig. 2 is an inner side structural view of Fig. 1, and Fig. 3 is an equivalent circuit diagram of Fig. 1 to 3, the conventional low-pass filter is formed of a box-like structure in which a cavity is formed through a housing 12 made of a metal such as aluminum (alloy) and a cover 12. In the example of FIG. 1 and FIG. 2, a rectangular box structure elongated in a transverse direction is shown. An input port 142 and an output port 144 may be respectively formed at portions corresponding to both ends of the box structure in the longitudinal direction and C elements C 1 and C 2 may be provided between the input port 142 and the output port 144. , C3, C4, C5, and C6 and the L elements L1, L2, L3, L4, and L5 are alternately formed. At this time, the C elements (C1-C6) and the L elements (L1-L5) alternately formed are structured to be connected in series in terms of mechanism.

1 to 3, the first C element C1 is connected to the input port 142 and then the first L element L1, the second C element C2, the second L element L2, The third C element C3, the third L element L3, the fourth C element C4, the fourth L element L4, the fifth C element C5, the fifth L element L5, C element C6 are connected in series and the sixth C element C6 and the output port 144 are connected.

The C elements (C1-C6) may be formed of a metal structure having a cylindrical shape, each of which is laid out so that the curved surface of the cylinder faces the inner surface of the housing 14 and the cover 12 to form a capacitance coupling surface . At this time, the heights of the cylinders may be appropriately different from each other in order to form an appropriate capacitance value for each of the C elements (C1-C6). The L devices L1 to L5 may be formed of a metallic fin structure which is provided between the C devices C1 to C6 and connects the C devices C1 to C6.

1 and 2, the L devices L1 to L5 are connected in series between the input port 142 and the output port 144, Respectively. The C elements C1 to C6 are respectively connected to the ground terminals at the connection points between the respective L elements L1 to L5 and at the input and output points of all the L elements L1 to L5, do.

In the low-pass filter configured as described above, each L element serves to pass only a low frequency band between the input port and the output port, and each C element plays a role of passing the high frequency band through the ground terminal . At this time, each of the L elements and the C elements forms a stage of the corresponding filter. Usually, the low-pass filter has a multi-stage structure using a plurality of L elements and a plurality of C elements, as shown in Figs. 1 to 3, so as to have a required filtering characteristic.

The C elements (C1-C6) and the L elements (L1-L5) are generally integrally formed by processing one base material by a die-casting method for improving the product characteristics and simplifying the manufacturing process.

However, since the low-pass filter having the above-described structure has a configuration in which the C elements and the L elements are mechanically connected in a line, the required length of the total length is considerably increased, There was a difficulty in designing the product.

Also, low-pass filters are typically fabricated in one piece with other components, for example, as a component in a wireless signal processing device. Since the low-pass filter has a coupling structure of a filter and a housing, it is necessary to design the position of the low-pass filter at the cover side of the main housing when designing the main housing of the radio signal processing equipment. There were many constraints in designing.

In addition, in the filter structure, a method of forming a notch (attenuation pole) in order to improve the skirt characteristic without increasing the number of stages of the filter is considered. In order to form a normal notch, a method of providing an additional auxiliary capacitance element or an inductance element between each end of the filter and the end of the filter has been proposed. As described above, the C elements and the L elements are mechanically arranged in a line It is difficult to form a notch in a low-pass filter having a configuration that is connected to a low-pass filter.

Accordingly, an object of the present invention is to provide a cavity-type low-pass filter capable of relatively reducing the total length and increasing the degree of design freedom, thereby making it easier to manufacture.

Another object of the present invention is to provide a cavity-type low-pass filter capable of providing a notch characteristic with a more efficient structure.

According to an aspect of the present invention, there is provided a low-pass filter of a cavity type; L (inductance) elements composed of a transmission line structure having an inductance component and connected in series; A housing forming a groove at a position corresponding to at least a part of an installation space of the L devices, connection points between the L devices and input and output of all L devices; And a capacitance coupling surface facing the inner surfaces of the grooves, wherein the connection points between the L elements and at least some of the points corresponding to the inputs and outputs of the L elements are directly or indirectly (Capacitance) elements connected to the input terminal.

At least some of the C devices may be indirectly coupled to connection points between the L devices and at least some of the points corresponding to the inputs and outputs of all L devices through an auxiliary L device that additionally provides inductance .

The grooves are formed in a circular shape, and the C elements are formed in a cylindrical shape so that the curved surface of the cylinder faces the inner surface of the corresponding circular grooves.

The overall structure of the filter stages formed by the L devices and the C devices may be symmetrically formed around the center point.

As described above, the cavity-type low-pass filter according to the present invention can relatively reduce the total length, increase the degree of freedom of design, and can be manufactured more easily, and can provide notch characteristics with a more efficient structure .

1 is a perspective view of a conventional low-pass filter of a cavity type;
Fig. 2 is a side view of the inner side structure of Fig. 1
Fig. 3 is an equivalent circuit diagram of Fig.
4 is a perspective view of a cavity-type low-pass filter according to an embodiment of the present invention.
Fig. 5 is a side view of the inner side structure of Fig. 4
Fig. 6 is an equivalent circuit diagram of Fig. 4
Fig. 7 is a graph showing the filtering characteristics of Fig. 4
FIG. 8 is a perspective view showing a modified structure of the filter of FIG.
Fig. 9 is an internal side structural view showing another modified structure of the filter of Fig. 4

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following drawings, the same constituent elements are given the same reference numerals as possible.

FIG. 4 is a perspective view of a cavity-type low-pass filter according to an embodiment of the present invention, FIG. 5 is an internal side view of FIG. 4, and FIG. 6 is an equivalent circuit diagram of FIG. 4 to 6, a low-pass filter according to an embodiment of the present invention includes a metal housing 22 (indicated by a box of a single dotted line in the example of FIG. 4) made of aluminum Thereby forming a cavity (indicated by a dotted box in the example of Fig. 4).

4 and 5, the housing 22 is basically formed with a rectangular box structure in which the cavity is elongated in the transverse direction. The cavity includes a plurality of grooves G1, G2 and G3 , G4, G5, G6) is further formed to extend downwardly from the bottom of the cavity, for example. An input port 222 and an output port 224 may be respectively formed at portions corresponding to both ends of the housing 22 in the longitudinal direction and L elements L1 , L2, L3, L4, L5) are mechanically and circuitly connected in series.

The L devices (L1-L5) may be connected in a linear form as a whole, for example, and may have a transmission line structure similar to a strip line, and may be integrally formed. The length of each of the L elements L1 to L5 is suitably designed in advance so as to have a required inductance value. At this time, the cavity is set to an appropriate size in consideration of the electrical characteristics and installation space of the L devices (L1-L5). 4 and 5, the shape, length, thickness, and the like of each of the L elements L1 to L5 are formed to be the same so as to have the same low-frequency band pass characteristics. However, in each of the L elements L1 to L5 The shape, length, thickness, and the like may be appropriately (differently) designed so as to form an overall low-pass characteristic by a combination of the inductance components thereof.

In addition, at least a part of the input points and the output points of all the L elements (L1 to L5) (all points in the examples of FIGS. 4 and 5) and the connection points between the respective L elements For example, circular grooves (G1-G6) are formed. The grooves G1-G6 are provided to provide a space for installing the C elements C1, C2, C3, C4, C5, and C6, respectively. The C elements C1- The curved surface of the cylinder facing the inner surfaces of the corresponding grooves G1-G6 to form a capacitance coupling surface. At this time, the heights of the cylinders may be appropriately different from each other in order to form an appropriate capacitance value for each of the C elements (C1-C6). In the example of FIGS. 4 and 5, for example, the first C element C1 is shorter in length than the second C element C2, so that the first C element C1 is the second And is designed to have a smaller capacitance than the C element C2. In addition, each shape, length or thickness of the C elements (C1-C6) can be designed appropriately (differently) so as to have a required capacitance value, and likewise, the corresponding grooves (G1-G6) The shape, depth, diameter and the like of the substrate can also be appropriately designed (different from each other).

Each of the C elements C1 to C6 may be directly attached by soldering or welding at a connection point with the L elements L1 to L5. However, according to an embodiment of the present invention, (Ln1, Ln2, Ln3, Ln4, Ln5, Ln6). The auxiliary L devices Ln1 to Ln6 are for forming a notch characteristic in the corresponding filter by providing an additional inductance in the C-stage, as shown in Fig.

The auxiliary L elements Ln1 to Ln6 are provided between the connection point with the L elements L1 to L5 and the C elements C1 to C6 to connect the C elements C1 to C6 to the L element And may be formed in a pin structure of a metal that is connected to a connection point between the first and second electrodes L1-L5. The shape, length or thickness of each of the auxiliary L devices Ln1 to Ln6 may be designed appropriately (differently) in advance so as to have a required inductance value. In the examples of FIGS. 4 and 5, for example, the first auxiliary L element Ln1 has a longer length and a smaller thickness than the second auxiliary L element Ln2, Ln1 is designed to have a larger inductance value than the second auxiliary L element Ln2. The auxiliary L devices Ln1-Ln6 may be soldered or welded to the connection point with the L devices L1-L5.

When the L elements L1 to L5 and the C elements C1 to C6 are arranged in a mechanical structure, the C elements C1 to C6 are arranged side by side between the L elements L1 to L5 It can be regarded as being installed in a branched manner. At this time, at least a part of the C elements (C1-C6) can be viewed as a structure indirectly installed by the auxiliary L elements (Ln1-Ln6) to form a notch characteristic.

4 to 6, the first through fifth L-elements L 1 through L 5 are sequentially connected to one line between the input port 222 and the output port 224, The first C element C1 is branched and connected to the connecting portion of the first L element L1 and the second L element L1 through the connecting portion between the first and second L elements L1 and L2, The third C element C3 is connected to the connection portion between the second and third L elements L2 and L3 and the fourth C element is connected to the connection portion between the third and fourth L elements L3 and L4, The fifth C element C5 is branched and connected to the connection portion between the fifth L element L5 and the output port 224 and the fifth L element L5 is connected to the connection portion between the fifth L element L4 and the fifth L element L4, And the sixth C element C6 is connected in a branched manner.

At this time, the first to sixth C-elements (C1 to C6) are provided in the first to sixth grooves (G1 to G6), and are designed so as to have symmetrical capacitance values about the center point of the entire filter structure . That is, the first and sixth C elements C1 and C6 are equal to each other, for example, designed to have the lowest capacitance value, and the second and fifth C elements C2 and C5 are equal to each other and the intermediate capacitance And the third and fourth C elements C3 and C4 are designed to have the same value and have the highest capacitance value.

In addition, the lengths of the auxiliary L devices Ln1 to Ln6 can be appropriately (differently) designed to have symmetrical capacitance values about the center point of the filter. For example, the first and sixth auxiliary L devices Ln1 and Ln6 are equal to each other, and are designed to have the highest inductance value, for example, and the second and fifth auxiliary L devices Ln2 and Ln5 And the third and fourth auxiliary L devices Ln3 and Ln4 are equal to each other and have the lowest inductance value (for example, 0). 4 and 5, the reference symbols for the third and fourth auxiliary L devices Ln3 and Ln4 are separately shown. However, for convenience of explanation, when the inductance value is set to 0, Mechanically, it will be understood that the auxiliary L element is not actually installed, and that the C element is a structure directly attached to the connection point with the L elements.

 At this time, the depths of the grooves G1-G6 may be similarly designed differently symmetrically with respect to each other. In this way, when the structures of the respective stages of the low-pass filter are symmetrically produced, uniform characteristics can be obtained in the pass band (low band) of the low-band pass filter.

4 and 5, the input port 222 is connected to the first L element L1, and the fifth L element L5 and the output port 224 are connected to each other through a predetermined type of matching panel for impedance matching 226, 228 are additionally shown.

4 and 5, in order to appropriately support the L devices L1 to L5, the C devices C1 to C6, or the auxiliary L devices Ln1 to Ln6, Or the like may be additionally provided. For example, such a support structure may have a structure in which it is mounted so as to be fitted in the corresponding grooves G1-G6 while surrounding the C-elements C1-C6.

As shown in FIGS. 4 to 6, the structure of the low-pass filter according to an embodiment of the present invention includes a structure in which L elements and C elements are structured mechanically, for example, in the horizontal direction The structure according to the present invention is arranged such that the L elements are arranged in the lateral direction but the C elements are arranged in the longitudinal direction so that the lateral It is possible to reduce the length of the direction (total length).

In FIGS. 4 and 5, the illustration of the cover is omitted. In a practical product, a structure corresponding to the cover may be provided to seal the opening portion of the housing. However, the structure according to an embodiment of the present invention is a structure that does not greatly affect the filtering operation even if the structure is not provided with a cover. That is, in the structure of the conventional low-pass filter as shown in FIGS. 1 and 2, since the C elements must perform a capacitance coupling action between the housing and the cover, the cover must be provided in a specific region. However, The invention has a structure in which the C elements perform a groove-capacitance coupling action, and the effect of the cover on the L and C elements is small, so that the position of the cover can be freely arranged. The structure according to the present invention can be used, for example, as a component in a wireless signal processing equipment, when the main housing of the wireless signal processing equipment is designed as one unit with other components, It is not necessary to design the cover side of the main housing, and it is possible to provide a wide degree of freedom in product designing.

Also, as in the structures shown in FIGS. 4 to 6, in the present invention, it is easy to install a separate auxiliary L element for each C element, and conventional C elements and L elements are mechanically Compared to a structure connected in series, it can be very easy to form the notch characteristic.

7 is a graph showing the filtering characteristics of FIG. Referring to FIG. 7, low-pass characteristics of a low-pass filter according to an embodiment of the present invention can be seen. For example, as shown in FIG. 7, the low-pass filter of the present invention has a good low-pass characteristic at about 2.7 GHz band or less and a notch characteristic of about 90 dB or more is formed at about 4.1 GHz.

As described above, the cavity-type low-pass filter according to the embodiments of the present invention can be configured. In addition, various other embodiments and modifications may be made. For example, in the above description, the L elements are described as being connected in a line in a linear form as a whole, but the entire connection form of the L elements may be at least one or more times And may be implemented so as to be connected in a form of being bent (for example, in the form of 'a', 'c', 'd').

FIG. 8 is a perspective view showing a modified structure of the filter of FIG. 4, and in the modified structure of FIG. 8, the L elements L1-L6 are connected in a 'C' shape as a whole. Correspondingly, a plurality of grooves G1-G6, a plurality of C elements C1-C6, a plurality of auxiliary L devices Ln1-Ln6, etc., including the housing 22, are suitably formed. At this time, it will be understood that the filter structure shown in Fig. 8 may be the same circuit as shown in Fig.

8, the input port 222 and the output port 224 may be formed on the same surface of the housing 22. [ This can provide a more appropriate structure in some cases in actual product implementation.

8, the third L element L3 is longer in length than the other L elements L1-L2 and L4-5 and has a larger thickness Sectional area is wider). Thus, the length and thickness of the L element can be designed appropriately (unlike other L elements) so as to have a required inductance value.

In the above description, the diameters of the C-shaped C-shaped elements are all the same, but the diameters of the C-shaped elements can be different from each other (at least partly) Can be configured. 9 shows an inner side structural view showing another modified structure of the filter of Fig. 4. In Fig. 9, for example, the first and sixth C elements C1 and C6 are connected to the other C elements C2-C5 , The diameter of the first groove G1 and the diameter of the sixth groove G6 are similarly formed to be smaller (accordingly, they have a smaller capacitance value). In addition, it is also possible to set the capacitance value by changing the diameter of either the C element or the groove (that is, by changing the distance between the C element and the groove). Thus, various modifications and variations of the present invention can be made without departing from the spirit and scope of the present invention as defined by the appended claims and their equivalents.

Claims (10)

In a low-pass filter of a cavity type,
L (inductance) elements constituted by a transmission line structure having an inductance component and connected in series;
A housing forming a groove at a position corresponding to at least a part of an installation space of the L devices, connection points between the L devices and input and output of all L devices;
And a capacitance coupling surface facing the inner surfaces of the grooves, wherein the connection points between the L elements and at least some of the points corresponding to the input and output of all the L elements are directly or indirectly (Capacitance) elements connected to the input terminal of the low pass filter.
The method of claim 1, wherein at least some of the C elements
And indirectly connected to at least some of the points corresponding to the input and output of all the L elements via connection points between the L elements via an auxiliary L element that additionally provides inductance.
3. The method of claim 2,
Wherein the auxiliary L device is formed in a pin structure having an inductance component.
The method of claim 3,
At least one of the auxiliary L devices is different in length or thickness from the other auxiliary L devices.
The method according to claim 1,
Wherein at least one of the L elements is different in length or thickness from the other L elements.
The method according to claim 1,
Wherein the plurality of C elements are cylindrical,
Wherein the plurality of grooves accommodate the C-shaped element in a cylindrical shape, and the curved surface of the cylinder faces the inner surface of the groove.
The method according to claim 6,
Wherein at least one of the plurality of C elements is different from the other C elements in at least one of a length in the longitudinal direction or a diameter of the cylinder.
The method according to claim 6,
Wherein at least one of the plurality of grooves has at least one of a depth and a diameter of the groove different from the other grooves.
The method according to claim 1,
Wherein the overall structure of the filter stages formed by the L devices and the C devices is formed symmetrically with respect to the center point.
The method according to claim 1,
Wherein the overall connection form of the L devices is connected in series in at least one folded form.

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